1. Field of the Invention
This invention is related in general to multi-layer transparent flexible barriers and to processes of manufacture for such barriers. In particular, the invention pertains to a composite barrier produced by vacuum as well as atmospheric deposition and a modular approach for using such a flexible barrier to produce transparent enclosures for encapsulating a flexible device with progressively higher levels of environmental protection.
2. Description of the Related Art
Inorganic and polymeric coatings deposited under vacuum or atmospheric conditions have been used for some time to promote desirable properties for particular applications. Multi-layer coatings of various combinations of materials have also been used to enhance the effectiveness of the coatings. Most notably, such coatings have been used successfully as barriers to moisture and oxygen permeability in packaging for foods and electronic devices.
Inorganic barrier layers consist of thin films of metals or ceramics (such as aluminum oxide, silicon oxide, indium tin oxide, etc.) deposited onto appropriate substrates by a variety of known processes, most notably by sputtering, chemical vapor deposition or physical vapor deposition. Organic polymeric barriers may be similarly produced by evaporating monomers or oligomers in vacuum, depositing the vapor to produce a film over a substrate, and curing the film to form a polymeric barrier. Inorganic and organic layers are often combined in multi-layer barriers to decrease permeability and/or add further functionalities to the barrier structure.
Flexible barriers may be transparent or opaque. Transparent barriers are used in applications where the product needs to be visible or where light must enter or exit the enclosed package. Such applications include, for example, food, medical and chemical packages, information displays, lights, and photovoltaic devices. Flexible transparent barriers utilize a combination of polymer layers with thin inorganic coatings that are transparent. Opaque barriers are used in packages where light transmission is not necessary. Opaque barriers are commonly produced using metal foils, such as aluminum, laminated with polymer layers.
Barriers have also been produced by mixing inorganic materials, such as metals, oxides and other ceramics, in a liquid monomer/oligomer and curing it to form a polymeric composite that is then used as a barrier material. In the case of a thermoplastic polymer, the material may be applied as a coating by a variety of application processes, such as extrusion, drawdown or roll coating, over the article of interest. Thermoset polymers, on the other hand, are first deposited as a layer over the article and then crosslinked to form the desired barrier.
As barrier coatings have increasingly become a normal part of manufacturing processes, the specifications for low permeability to oxygen and moisture have also become more and more stringent. That is particularly true in the evolving field of flexible displays, photovoltaic devices and flexible solid-state lights that utilize organic light emitting diodes and corrosion sensitive electrode systems where enclosures with very high barrier levels are required. Current flexible barrier designs focus on the use of specific single or multi-layer barrier structures that are deposited or laminated onto a device that is fabricated on a similar barrier sheet. However, device fabrication on a barrier layer imposes additional limitations to the barrier sheet properties, such as temperature and thermo-mechanical stability. Therefore, there is a continuing need for improved barrier structures that can be used to meet different performance specifications as needed in a commercial environment and for improved methods of producing device enclosures that are independent of or can withstand device manufacturing conditions.